Study On Coupling Process Of High Temperature Microaerobic - Anaerobic Two - Stage Digestion

As the disposal capacity and requirements of sewage treatment turned higher and higher, sludge production was increasing. Autothermal thermophilic aerobic digestion(ATAD) was a kind of high efficient biological stabilization and harmless treatment technology, which had the advantages of short sludge retention time, rapid VSS reduction, efficient pathogen inactivation, faster starting, and good resistance of the low temperature impact of autumn and winter. Meanwhile, the digested sludge met each standard of sludge in China and the standards of Class A in Item 503 enacted by US EPA. But there were problems with no methane and worse dewatering performance. Anaerobic digestion process which produced methane was not suitable for medium and small sized sewage treatment plant on ground of long sludge retention time, and low digestive efficiency. TAD-MAD technology which combined the advantages of ATAD and mesophilic anaerobic digestion(MAD) has been developed with the independent intellectual property to enhance the sludge stabilization efficiency, shorten the residence time, improve the dewatering performance, and produce methane gas.To study the running stability, gas production performance and dewatering performance of digestion sludge of TAD-MAD with high solid content, the urban sewage sludgr was treated with TAD-MAD sequencing batch reactor. Meanwhile compared to MAD process and TAD process. The results showed that the optimum conditions of TAD-MAD technology were obtained as follow: TSS was 7.1%, the temperature of themophilic system was 55℃, HRT was 2d, the mesophilic temperature was 35℃, HRT was 22 d, the HRT of TAD-MAD process was 24 d. Under these conditions, sludge digestion efficiency was the best. The VSS removal rate reached above 40% after 20 days of digestion reaction, whlie it was 29.9% of MAD process, and didn’t even reach 40% until the end of the digestion. In addition, TAD-MAD process was superior to MAD process in cumulative gas production and cumulative methane production until the end of the digestion with 149.2m L/g VSS and 116.6 m L/g VSS respectively. On day thirteenth, the content of methane of TAD-MAD process was stable between 75.4% and 79.1%. The results about the dewatering performance of digestion sludge of TAD-MAD process showed that TAD-MAD process improved the sludge dewatering performance effectively.In conclusion, TAD-MAD process had the advantages of short sludge retention time, rapid VSS reduction, a high rate of methane gas production and owned better dewatering performance.